This thesis deals with various properties of the 3He A-8 phase
boundary. First a review of some static properties, the surface energy
and Kapitza resistance, is given. Then the symmetry of the interface is
discussed. It is pointed out that, due to the presence of the condensate,
many symmetries are broken. The effects of this are discussed; in
par ticular it is shown that a transverse force acting across the boundary
will result if a temperature difference exists between the two bulk
phases. Finally the dynamics of the phase boundary is discussed via a
phenomenological equation of motion. The higher temperature
dissipative mechanism is ascribed to the Andreev scattering of
excitations with the boundary. The predicted terminal velocity of the
interface when the phases are hypercooled is shown to agree with
experiment. The lower temperature dissipative mechanism is proposed
to be pair-breaking, and a saturation of the terminal velocity at low
temperatures is predicted.